Comparative nectar dynamics in four ornithophilous Melocactus (Cactaceae) species in a seasonally dry tropical forest

Nectar is an important floral resource, often representing the only source of water for pollinators in arid environments. We investigated whether successive nectar removal would affect the nectar production dynamics of four Melocactus species growing in the Caatinga domain. Nectar was serially extracted from flowers four times per day at regular 60-min intervals after anthesis. The cactus species showed a consistent pattern of secretion linked to ornithophily, with no significant responses to successive nectar removal and no reabsorption. Nectar secretion covered the entire period of anthesis, starting at 2:30 p.m. and continuing to 5:30 p.m., with the production of 11-38 mu l per flower, with sugar concentrations of 10%-32% (3-16 mg of sugar). Individual flowers produced average amounts of 16.9-3.43 mg of sugar per day, corresponding to energy values of 0.06-0.28 kJ. Sympatric populations produced an average of 150-200 flowers per day. The nectar produced by Melocactus can therefore meet the daily energy needs of hummingbirds, which is of special importance during the dry season, when resources are scarce in the Caatinga.